Carburetors have been used to produce and control the delivery of a fuel and air mixture to an internal combustion engine. Some carburetors have a main body with an air intake passage extending therethrough and a throttle valve disposed in the air intake passage. The throttle valve is movable between an idle position and a wide open throttle position to control the flow of air through the carburetor.
In so-called butterfly-type carburetors, the throttle valve comprises a generally flat disk rotatable in the intake passage to vary the effective flow area of the air intake passage. Rotation of the throttle valve permits a vacuum pressure signal to act as a function of the position of the throttle valve on a plurality of fuel jets opening into the air intake passage. Thus, movement of the throttle valve controls the flow of fuel out of the various fuel jets whereupon the fuel is mixed with air flowing through the air intake passage. The fuel and air are mixed in the air intake passage and subsequently delivered to an engine to support its operation.
In so-called rotary throttle-type carburetors, a valve chamber extends perpendicular to the air intake passage and a cylindrical throttle valve shaft is received in the valve chamber. A hole through the throttle valve shaft is increasingly aligned with the air intake passage as the throttle valve is rotated from its idle position towards its wide open throttle position to control air flow in the carburetor. A needle carried by the throttle valve shaft is moved relative to a fuel nozzle as the throttle valve is rotated, to vary the effective flow area of the fuel nozzle. In this manner, the flow rate of fuel is adjusted according to the position of the throttle valve, and fuel discharged from the fuel nozzle mixes with air in the air intake passage for delivery of a fuel and air mixture to the engine.